Sintered hard metal alloy and articles made thereof



"Patented June 30, 1931 UNITED STATES PATENT OFFICE v BENNO s'rmuss, or ESSEN, GERMANY, AsSIGNoB, BY mnsNn ASSIGNMENTS, 'ro GEN- Em nnnc'rmc courANY, A ooarona'rroN or NEW YORK SI'NTERED HARD METAL ALLOY AND ARTICLES MADE THEREOF EHO Drawing. Application filed April 14, 1927,S eria1 No. 183,899, and in Germany October 25, 1926.

This invention relates to hard metal alloys and articles made thereof,.such as tools and implements, which alloys do not show pores in the fracture, in for instance a fiftyfold magnification. This invention also relates to a process for producing these alloys. By hardmetal alloys I mean alloys including metals having a melting point above 2000 U.

Alloys of this nature. and articles made 19 thereof, such as tools and implements, are dis tinguished from the known sintered hard metal alloys, and tools and implements made thereof, especially by the fact that they possess, besides the extraordinary hardness 1!! characteristics of alL hard metal alloys, a strength and tenacity" not obtained hitherto, so that for instance turning tools made of my novel alloys resist with certainty-the shock like stresses unavoidable in the operation of 2o machine tools.

As an example of the realization of my invention, I shall point out in the following the manner in which a hard metal alloy is produced which appears imporous inf fifty- 25 fold magnification and contains, besides carbide of tungsten, per cent of cobalt;

Firstly the appropriate quantities of tungsten metal and cobalt metal are ground separately in a ball mill or the like so that the so size of each particle of tungsten metal and of cobalt metal becomes smaller than 1 x mm. The finely ground tungsten metal is then carburated in a graphite crucible with a slight excess of carbon in a gas heated furnace in an oxidizing atmosphere, whereby a carbide of tungsten is produced which is entirely free from graphite and has a content of carbon of about 5.2 to 6.2 per cent. Of course, the carburation may be performed in another way. The tungsten carbide obtained is ground anew in a ball mill so that the size of the particles again becomes smaller than 1 x 10" mm. This fine tungsten carbide powder is then intimately mixed with a binder material such as the fine cobalt powder and the mixture is subjected to a further grinding operation of very long duration, (at least hours). By this third grinding operation a much more intimate mixture of 50 the mixed powder and a further reduction of the grain size is obtained. After the third gr nding operation has been terminated, the mixture is in a condition in which apparently each carbide particle is enveloped by a very thin cobalt pellicle. For the purpose of manufacturing a tool, a pressed body is then made of the-powder mixture thus produced whlch body has the approximate finished shape of the desired tool. This pressed body is converted into a tool having the desired 00 finished shape by a preliminary sintering operation at about 700 to 1100 degrees (1., a

subsequent working operation bymaterialdetaching means, to obtain the exact finished shape, and by a high temperature sintering process at about- 1300 to 1600 degrees (3. This tool possesses besides an extraordinary hardness a strength and tenacity hitherto not obtained. This exceedingly high strength and tenacity of-the alloy is due to the fact 0 that the alloy has an imporous appearance in the fracture even in for instance a fiftyfold magnification.

The employment of the above-mentioned third grinding operation results in a particularly dense and correspondingly resistant product. What I claim as my invention and desire o secure by Letters Patent, is

1. The process of making articles of hard metal alloys having a fracture exhibiting an imporous texture at fifty-fold magnification which comprises mixing a heavy metal carbide powder of a grain size smaller than 1 x 10' mm. with a softer metal powder of a grain size smaller than 1 x 10" mm., grinding this mixture for at least fifty hours, pressing shapes of the mixture and sintering them at a temperature below the volatilizing tempera.- ture of the softer met-a1.

2. The process of making articles of hard metal alloys having -a fracture'exhibiting an imporous texture at fifty-fold magnification which comprises mixing a tungsten carbide powder 'of a grain size smaller than 1 x 10' mm. with a softer metal powder of a shapes of the mixture and sintering them at a temperature below the volatilizing temperature of the softer metal.

3. The method of forming a metal working tool which comprises ball milling a composition consisting mainly of finely divided hard metal carbide particles but containing an appreciable but minor quantity of a finely divided binder metal having-a lower melting point than said carbide, said ball milling being continued until substantially each of said carbideparticles are enveloped by a pellicle of said binder metal, pressing the milled material into shapes and sintering them at a temperature below the volatilization temperature of said binder metal.

4. The method of forming a metal working tool which comprises ball milling a composition consisting mainly of finely divided hard metal carbide particles but containing an appreciable but minor quantity of finely divided metal of the iron group, said ball milling being continued until substantially each of said carbide particles are enveloped by a pellicle of said metal of the iron group, pressing the milled material into shapes and sintering them at a temperature below the volatilization temperature of said metal of the iron group.

5. The method of forming a metal working tool which comprises ball milling a composition consisting substantially of finely divided tungsten carbide particles but containing an appreciable but minor quantity of finely divided cobalt, said ball milling being continned until substantially each of the carbide particles are enveloped by a cobalt pellicle, pressing the milled material into shapes and sintering them at a temperature below the volatilization temperature of said cobalt.

6. The method of forming a metal working tool which comprises ball milling for at least fiftv hours a composition consisting substan tially of finely divided hard metal carbide particles but containing an appreciable but minor quantity of a finely divided metal of the iron group, pressing the milled materials into shapes and sintering them at a temperature below the volatilization temperature of said metal of the iron group.

7. The method of forming a metal Working tool which comprises ball milling for at least fifty hours a composition consisting substantially of finelydivided tungsten carbide particles but containing an appreciable but minor quantity of finely divided cobalt,

pressing the milled materials into shapes and sintering them at a temperature below the volatilization temperature of said cobalt.

The. foregoing specification signed at Coqlpgne, Germany, this 18th. day of March,

1 BENNO STRAUSS. 

